Contribution of Streptococcus thermophilus to Growth-Stimulating Effect of Yogurt on Rats

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Abstract
The origin of the growth-stimulating factor in yogurt was studied in rats fed liquid or freeze-dried diets of milk, yogurt, milks fermented individually by S. thermophilus and Lactobacillus bulgaricus, and milks to which cells of S. thermophilus and L. bulgaricus were added. Diets containing sonicated cells, cell supernatant and cell fractions also were fed. Milk fermented by S. thermophilus and milk plus S. thermophilus cells stimulated growth as effectively as did yogurt. That finding and the absence of stimulation in rats fed L. bulgaricus showed that S. thermophilus is responsible for stimulation of growth by yogurt. Growth was stimulated by an intracellular factor and not by fermentative changes in the milk.
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